Temperature-Insensitive Humidity Sensor Based on a Silica Fiber Taper Interferometer

A relative humidity (RH) sensor based on a silica fiber taper interferometer is proposed and demonstrated. The interferometer is formed by simply tapering a double cladded fiber down to 3.8 μm in diameter. The two transition regions excite energy transfers between the fundamental mode and higher-order mode and act as beam splitter and combiner, respectively. Interferometric fringes can therefore be observed in the transmission spectrum due to the phase difference between the two modes over the uniform region. RH measurement is carried out by monitoring the spectral shift of the fringes induced by the evanescent-field interaction. The sensor presents a sensitivity to surrounding RH of 97.76 pm/%RH and a temperature sensitivity as low as 4.74 pm/
^°
C. It can respond to RH change within 188 ms. Compared with previous reports, the present RH sensor does not need extra functional coating and exhibits advantages including fast response, temperature insensitivity, and low manufacture cost.